GGT and 5'-NT

Gammaglutamyltransferase (GGT)

1. Located primarily in hepatocytes and to a lesser extent in a number of other organs

2. Highly sensitive to hepatocyte damage and cholestasis

3. Elevated in chronic alcohol consumption and binge drinking

4. Also elevated by extensive reparative processes, drugs (phenytoin and phenobarbital), obesity

5. Not elevated by bone disease, pregnancy, or childhood and adolescence

6. Used as a confirmatory test to indicate a hepatic origin for ALP elevation (GGT can be elevated in co-existing conditions, so interpret its results carefully and with consideration of the whole clinical picture)

5'-Nucleotidase

1. Provides confirmation for a hepatic origin for elevated ALP similar to GGT

2. More specific for the liver and for cholestasis than GGT (which is generally elevated with any type of hepatocellular injury)

3. Controversial as to whether GGT or 5'-NT provides the best confirmatory test; in the past, 5'-NT has been more difficult to perform and thus less generally available